Wavelength modulation to improve optical link bit error rate

ABSTRACT

An optical transceiver module includes an optical transceiver and a controller. The optical transceiver has a ring filter configured to transmit optical signals from or receive optical signals for the optical transceiver module. The controller is configured to: detect a carrier frequency at the optical transceiver; detect a data signal frequency of data at the optical transceiver; determine a bit error rate of the data; and in response to determining that the bit error rate of the data is greater than a threshold, periodically vary a central wavelength of the ring filter at a frequency at least three orders slower than the data signal frequency.

DESCRIPTION OF RELATED ART

An optical network generally includes an optical transmitter, an opticalreceiver, and an optical fiber connected therebetween. Signaltransmissions between nodes of the optical network may be impeded due toerrors at transmitters, receivers, and/or optical cables. The errors canbe measured by a bit error rate as an indication of how reliable thesignal transmissions in the network are.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure, in accordance with one or more variousembodiments, is described in detail with reference to the followingfigures. The figures are provided for purposes of illustration only andmerely depict typical or example embodiments.

FIG. 1 is a block diagram illustrating an optical communication networkconfigured to implement techniques for reducing bit error rates,according to one embodiment.

FIG. 2A is a diagram illustrating carrier and data signals (solid line)of a transmitter ring filter and a resonant signal (broken line) of areceiver ring filter of a conventional optical communication network.

FIG. 2B is a diagram graphically illustrating spectral filtering of theconventional optical communication network of FIG. 2A.

FIG. 3A is a diagram illustrating carrier and data signals (solid line)of a transmitter ring filter and resonant signals (broken line) of areceiver ring filter of an optical communication network according toone example embodiment of this disclosure.

FIG. 3B is a diagram graphically illustrating spectral filtering of theoptical communication network of FIG. 3A.

FIG. 4A is a diagram illustrating carrier and data signals (solid line)of a transmitter ring filter and a resonant signal (broken line) of areceiver ring filter of another optical transceiving mechanism accordingto one example embodiment of this disclosure.

FIG. 4B is a diagram graphically illustrating spectral filtering of theoptical communication network of FIG. 4A.

FIG. 5A is a diagram illustrating carrier and data signals (solid line)of a transmitter ring filter and resonant signals (broken line) of areceiver ring filter of yet another optical transceiving mechanismaccording to one example embodiment of this disclosure.

FIG. 5B is a diagram graphically illustrating spectral filtering of theoptical communication network of FIG. 5A.

FIG. 6 is a block diagram illustrating another optical communicationnetwork configured to implement techniques for reducing bit error rates,according to one embodiment of this disclosure.

FIG. 7 is a block diagram illustrating yet another optical communicationnetwork configured to implement techniques for reducing bit error rates,according to one embodiment of this disclosure.

FIG. 8 is a block diagram of a ring filter according to one exampleembodiment of this disclosure.

The figures are not exhaustive and do not limit the present disclosureto the precise form disclosed.

DETAILED DESCRIPTION

Disclosed is an optical communication network. The optical interconnectsin the optical communication network may have a carrier frequency thatis, for example, in the 200 THz range, using a 1310 nm wavelength lightsource. A gigahertz level data rate can then be encoded onto the carriersignal. In this example, the carrier frequency and data signal frequencyare three orders of magnitude apart.

The optical interconnects may be implemented with ringresonators/filters. For example, a ring filter may be disposed at thereceiver to demultiplex an incoming signal. This signal is then routedto a photodetector that is at the drop port of the 4-port ringfilter/resonator. This approach results in the spectral filtering thatis caused by the drop port. The spectral filtering causes reducedrise/fall time in the output port, thus increasing bit error rate (BER).The techniques disclosed herein may ameliorate this disadvantage, asdescribed below.

Reference is now made to FIG. 1. FIG. 1 illustrates an opticalcommunication network 100 that includes two or more nodes. A topographyof the optical communication network 100 may be one-to-one, one-to-many,or many-to-many. In the illustrated example, the optical communicationnetwork 100 includes a first node 102 and a second node 104. The firstnode 102 and the second node 104 are lined with optical cables 106 a,106 b. Although shown as separate cables, the optical cables 106 a, 106b may be combined as a single duplex cable. Other types of cables may beemployed.

The first node 102 includes transceivers (e.g., optical transceivers oroptical transceiver modules “XCV”) 110, 112 and an application-specificintegrated circuit (ASIC) 114. The ASIC 114 includes a data output block(Data Out) 116, a data input (Data In) block 118, and a BER Count block120. The BER Count block 120 is connected to data input transceiver 112.The transceivers 110 and 112 include ring filters 122 and 124,respectively. The data output block 116 of the ASIC 114 is configured togenerate electrical signals to be transmitted by the transceiver 110.The electrical signals are converted into optical signals at thetransceiver 110 and transmitted through the ring filter 122 to thesecond node 104 via the optical cable 106 a. It is to be understood thatalthough the transceivers 110 and 112 are shown as separate unites, insome implementations, they can be integrated as one unit. In someembodiments, each of the transceivers 110, 112 may be implemented bysilicon photonic technologies.

The transceiver 112 is configured to receive optical signals through thering filter 124 and to convert the received optical signals intoelectrical signals for the ASIC 114. The data input block 118 of theASIC 114 receives the electrical signals from the transceiver 112. Thedata input block 118 may send the electrical signals to other functionalblocks of the ASIC 114 for processing. One of such functional blocks maybe the BER count block 120. The BER block 120 is configured to determinea BER for the received signals. For example, a count for bit errors inreceived digital signals over a period of, e.g., 1000 bits may becollected to determine the BER. When the BER is greater than athreshold, the BER count block 120 is configured to generate and send acontrol signal to the transceiver 112 to vary a central wavelength ofthe ring filter 124. In some embodiments, the threshold may bedetermined based on whether a forward error correction (FEC) is employedin the network. For example, the threshold may be about 10⁻⁵ when theFEC is employed or about 10⁻¹⁰ to 10⁻¹⁴ when the FEC is not implementedin the network. Once the BER count block 120 determines that the BER ofthe incoming signals is greater than a threshold, the BER count block120 may provide a control signal to the transceiver 112 to periodicallyvary a central wavelength of the ring filter 124. For example, the BERcount block 120 may provide the control signal to the transceiver 112 ata frequency of 1 kHz to several MHz. The central wavelength of the ringfilter 124 may be varied based on a data signal frequency of incomingdata signals. In some embodiments, the central wavelength of the ringfilter 124 may be varied at a frequency at least three orders slowerthan the data signal frequency.

Similarly, the second node 104 includes transceivers 130, 132 (e.g.,optical transceivers or optical transceiver modules “XCV”) and an ASIC134. The ASIC 134 includes a data output block 136, a data input block138, and a BER count block 140. The BER count block 140 is connected tothe transceiver 132 at the data input end. The transceivers 130 and 132include ring filters 142 and 144, respectively. The data output block136 of the ASIC 134 is configured to generate electrical signals to betransmitted by the transceiver 130. The electrical signals are convertedinto optical signals at the transceiver 130 and transmitted through thering filter 142 to the first node 102 via the optical cable 106 b.Although the transceivers 130 and 132 are shown as separate unites, insome implementations, they can be integrated as one unit. Each of thetransceivers 130, 132 may be implemented by silicon photonictechnologies.

The transceiver 132 is configured to receive optical signals through thering filter 144 and to convert the received optical signals intoelectrical signals for the ASIC 134. The data input block 138 of theASIC 114 receives the electrical signals from the transceiver 132. Thedata input block 138 may send the electrical signals to the BER countblock 140. The BER block 140 is configured to determine a BER for thereceived signals. When the BER is greater than a threshold, the BERcount block 140 is configured to generate and send a control signal tothe transceiver 132 to vary a central wavelength of the ring filter 144.For example, once the BER count block 140 determines that the BER of theincoming signals is greater than the threshold, the BER count block 140may provide a control signal to the transceiver 132 to periodically varya central wavelength of the ring filter 144. The central wavelength ofthe ring filter 144 may be varied based on a data signal frequency ofincoming data signals. In some embodiments, the central wavelength ofthe ring filter 144 may be varied at a frequency at least three ordersslower than the data signal frequency.

These techniques are further illustrated with greater detailshereinafter. FIG. 2A is a diagram illustrating carrier and data signals(solid line) of a transmitter ring filter and a resonant signal (brokenline) of a receiver ring filter of a conventional optical communicationnetwork. A transmitter (e.g., of a transceiver 110 or 130) is configuredtransmit a carrier signal 202 and data signals 204 a and 204 b. Thecarrier signal 202 has a central wavelength at a frequency f1, while thedata signals 204 a and 204 b each have a central wavelength atfrequencies f2 and f3, respectively, in FIG. 2A. For example, when thecarrier signal is at 2.282 THz (1310 nm) (e.g., f1) and the incomingdata is modulated at 20 Gbps with the carrier signal, optical side bandsmay fall at 2.262 (e.g., f2) and 2.302 THz (e.g., f3). For a typicaldense wavelength division modulation (DWDM) optical link, a resonantsignal 206 of a receiver ring filter (e.g., ring filter 124, 144 inFIG. 1) has a full width half maximum (FWHM) of about 25 GHz. Logically,the resonant signal 206 of the receiver ring filter may function as theoptical passband such that any optical signal outside of the resonantsignal 206 would be heavily attenuated. In general, the FWHM of 25 GHzis selected as a function of channel spacing, which is typically on theorder of 50-80 GHz. An optical passband may be selected 2-3 times lessthan the channel spacing. In this example, the receiver ring filter,tuned to 2.282 THz same as the carrier signal 202, would attenuate anysignal outside of frequency of 2.2695-2.2945 THz (i.e., 2.282 THz±25GHz). The optical sidebands (204 a′, 204 b′) due to modulation at 20Gbps, namely 2.262 and 2.302 THz, are outside of the bandpass andsuffers attenuation as shown in FIG. 2B.

The techniques disclosed herein allow periodically varying the centralwavelength of the ring filter at the transmitter and/or the receiversuch that the optical sidebands of the data signals can be received withless attenuation, which in turn may improve the bit error rate. FIG. 3Ais a diagram illustrating carrier and data signals (solid line) of atransmitter ring filter and resonant signals (broken line) of a receiverring filter of an optical communication network according to oneembodiment of this disclosure. The carrier signal 302 and the datasignals 304 a, 304 b of a transmitter (e.g., transceivers 122, 142) areshown in solid lines in FIG. 3A. The resonant signal 306 of the ringfilter at a receiver (e.g., ring filter 124, 144 in FIG. 1) is shown indotted lines. A central wavelength of the resonant signal 306 of thering filter is varied as shown by an arrow 310 by an offset A from thecenter of the carrier signal 302. For example, the central wavelength ofthe resonant signal 306 at the receiver ring filter is initially atfrequency f4, and is moved to frequency f5, back to frequency f4, and tofrequency f6, and back to frequency f4, and so on.

In some implementations, the central wavelength of the resonant signal306 is varied at a frequency at least three orders slower than the datasignal frequency. For example, when the data signals are transmitted atgigahertz level, the frequency to vary the central wavelength of theresonant signal 306 may be set at kilohertz to megahertz range. Thistechnique allows the receiver to continue receive incoming data signalswithout significant decay.

The central wavelength of the resonant signal 306 can be sinusoidallyvaried in one embodiment. In another implementation, a centralwavelength of the resonant signal 306 can be varied with a controlsignal such as a ramp signal. For example, the control signal can movethe central wavelength of the resonant signal 306 at different speedswithin the offset A. While the central wavelength of the resonant signal306 may oscillate between frequencies f4-f6, it spends less time at thecenter frequency f4 and more time at end frequencies f5 and f6. Thecentral wavelength of the resonant signal 306 is moved at or aroundcenter frequency f4 at a speed greater than a speed at or around endfrequencies f5 and f6. This can be achieved by a bimodal drive mechanismto minimize the time in the center (f4) and maximize time at theendpoints (f5 and f6) with an exponential-mode control algorithm. Thebimodal drive mechanism may be refined with information of BER updatesin the network.

FIG. 3B is a diagram graphically illustrating data signals that havebeen modulated by the ring filter of the receiver, according to oneembodiment. Because the central wavelength of the resonant signal 306 isvaried, the power of the modulated data signals 304 a′ and 304 b′ arestronger than those (204 a′ and 204 b′) of FIG. 2B, improving thestrength of the received data signals. This leads to lower BER for thecommunication network.

In some implementations, a central wavelength of the receiver ringfilter may be stationary while a central wavelength of the carriersignal of the transmitter ring filter may be varied. An example isillustrated in FIG. 4A. In FIG. 4A, a central wavelength of the carriersignal 402 on the transmitter side is initially at, for example,frequency f7 and is moved to frequency f8, back to frequency f7, and tofrequency f9, and back to frequency f7, and so on, illustrated by anarrow 410. The central wavelength of the carrier signal 402 may besinusoidally varied with frequency f7 as a center. Because the datasignals 404 are encoded with the carrier signal 402, their centralwavelengths are also sinusoidally varied around frequency f7. Theresonant frequency 406 of the receiver ring filter is shown to center atthe frequency f7 without change.

In another implementation, a central wavelength of the carrier signal402 can be varied with a control signal such as a ramp signal. Forexample, the control signal can move the central wavelength of thecarrier signal 402 at different speeds. While the central wavelength ofthe carrier signal 402 may oscillate between frequencies f749, it spendsless time at the center frequency f7 and more time at end frequencies f8and f9. The central wavelength of the carrier signal 402 is moved at oraround center frequency f7 at a speed greater than a speed at or aroundend frequencies f8 and f9. This can be achieved by a bimodal drivemechanism to minimize the time in the center (f7) and maximize time atthe endpoints (f8 and f9) with an exponential-mode control algorithm.The bimodal drive mechanism may be refined with information of BERupdates in the network. Other control algorithm may be adopted if it canachieve the above effects.

The final data signal 404′ received at the receiver ring filter is shownin FIG. 4B. As compared to the attenuated data signals 204 a′, 204 b′ inFIG. 2B, the received data signal 404′ has stronger power, which in turncan reduce the BER.

In some other implementations, a central wavelength of the resonantsignal of the receiver ring filter and a central wavelength of thecarrier signal of the transmitter ring filter may both be varied. Anexample is illustrated in FIG. 5A. In FIG. 5A, a central wavelength ofthe carrier signal 502 on the transmitter side is initially at frequencyf10 and is moved to frequency 111, back to frequency f10, and tofrequency f12, and back to frequency f10, and so on, illustrated by anarrow 508. The central wavelength of the carrier signal 502 may besinusoidally varied around, for example, frequency f10. Because the datasignals 504 are encoded with the carrier signal 502, the centralwavelengths of the data signals 504 are also sinusoidally varied aroundfrequency f10. The resonant frequency 506 of the receiver ring filter isalso varied. For example, a central wavelength of resonant frequency 506of the receiver ring filter may be moved from frequency f10 to frequencyf11, back to frequency f10, and to frequency f12, and back to frequencyf10, and so on, illustrated by an arrow 510. The frequencies for varyingthe central wavelengths of the carrier signal 502 and the resonantfrequency 506 may be different and not synchronized to increase thechance that the data signals are modulated around the central wavelengthof the receiver ring filter. In some embodiments, a controller connectedto both the transmitter and the receiver may be provided to ensure thatthe central wavelengths of the carrier signal 502 and the resonantfrequency 506 does not coincide with each other. For example, thecentral wavelengths of the carrier signal 502 and the resonant frequency506 may be varied but kept away from each other at an offset.

As explained above, each of the central wavelengths of the carriersignal 502 and the resonant frequency 506 can be varied with a controlsignal such as a ramp signal. The control signal allows each of thecentral wavelengths of the carrier signal 502 and the resonant frequency506 to be moved in different speeds. While the central wavelength of thecarrier signal 502 may oscillate between frequencies f10-f12, it spendsless time at the center frequency f10 and more time at end frequenciesf11 and f12. The central wavelength of the carrier signal 502 is movedat or around center frequency f10 at a speed greater than a speed at oraround end frequencies f11 and f12. Similarly, while the centralwavelength of the resonant frequency 506 may oscillate betweenfrequencies f10-f12, it spends less time at the center frequency f10 andmore time at end frequencies f11 and f12. The central wavelength of theresonant frequency 506 is moved at or around center frequency f10 at aspeed greater than a speed at or around end frequencies f11 and f12.This can be achieved by a bimodal drive mechanism to minimize the timein the center (f10) and maximize time at the endpoints (f11 and f12)with an exponential-mode control algorithm.

The final data signals 504′ received at the receiver ring filter areshown in FIG. 5B. As compared to the attenuated data signals 204 a′, 204b′ in FIG. 2B, the received data signals 504′ have stronger power, whichin turn can reduce the BER.

FIG. 6 is a block diagram illustrating another optical communicationnetwork 600 configured to implement the techniques disclosed herein,according to one embodiment. The optical communication network 600includes a first node 602 and a second node 604. The first node 602 andthe second node 604 are connected to each other through optical cables606 a, 606 b. It should be understood that more nodes can be included inthe optical communication network 600. Although shown as separatecables, the optical cables 606 a, 606 b may be combined as a singleduplex cable.

The first node 602 includes transceivers (e.g., optical transceivers oroptical transceiver modules “XCV”) 610, 612 and an ASIC 614. The ASIC614 includes a data output block (Data Out) 616, a data input (Data In)block 618, and an RBC Count block 620. The transceivers 610 and 612include ring filters 622 and 624, respectively. The RBC Count block 620is coupled to the transceiver 610 to control data output. The dataoutput block 616 of the ASIC 614 is configured to generate electricalsignals to be transmitted by the transceiver 610. The electrical signalsare converted into optical signals at the transceiver 610 andtransmitted through the ring filter 622 to the second node 604 via theoptical cable 606 a. In some embodiments, each of the transceivers 610,612 may be implemented by silicon photonic technologies.

The transceiver 612 is configured to receive optical signals through thering filter 624 and to convert the received optical signals intoelectrical signals for the ASIC 614. The data input block 618 of theASIC 614 receives the electrical signals from the transceiver 612. Thedata input block 618 may send the electrical signals to other functionalblocks of the ASIC 614 for processing. The RBC block 620 is configuredto keep a count of data output. For example, the RBC block 620 may keepa rolling average of numbers of contiguous digital signals (1's or 0's)in a bitstream over a period of a predetermined bits (e.g., 1000 bits).The count may be used to determine a time or times to vary a centralwavelength of the ring filter 622. For example, the central wavelengthof the ring filter 622 may be varied each time the data output bit countreaches 1000 bits. Alternatively, a BER in the network 600 may be use tovary the central wavelength of the ring filter 622, which requires afeedback from node 604. When the ring count block 620 determines that itis time to vary central wavelength of the ring filter 622 or the BER isgreater than a threshold, the RBC count block 620 is configured togenerate and send a control signal to the transceiver 610 to vary acentral wavelength of the ring filter 622. The central wavelength of thering filter 622 may be varied periodically. The central wavelength ofthe ring filter 622 may be varied based on a data signal frequency ofthe data signals. In some embodiments, the central wavelength of thering filter 622 may be varied at a frequency at least three ordersslower than the data signal frequency.

Similarly, the second node 604 includes transceivers (e.g., opticaltransceivers or optical transceiver modules “XCV”) 630, 632 and an ASIC634. The ASIC 634 includes a data output block 636, a data input block638, and an RBC Count block 640. The RBC Count block 640 is coupled totransceiver 630 to control data output. The transceivers 630 and 632include ring filters 642 and 644, respectively. The data output block636 of the ASIC 634 is configured to generate electrical signals to betransmitted by the transceiver 630. The electrical signals are convertedinto optical signals at the transceiver 630 and transmitted through thering filter 642 to the first node 602 via the optical cable 606 b. Eachof the transceivers 630, 632 may be implemented by silicon photonictechnologies.

The transceiver 632 is configured to receive optical signals through thering filter 644 and to convert the received optical signals intoelectrical signals for the ASIC 634. The data input block 638 of theASIC 634 receives the electrical signals from the transceiver 632. Thedata input block 638 may send the electrical signals to the RBC countblock 640. The RBC block 640 is configured to keep a count of dataoutput for the node 604. For example, the RBC block 640 may keep arolling average of numbers of contiguous digital signals in a bitstreamover a period of a predetermined bits (e.g., 1000 bits). The count maybe used to determine a time or times to vary a central wavelength of thering filter 642. For example, the central wavelength of the ring filter642 may be varied each time the data output bit count reaches 1000 bits.Alternatively, a BER in the network 600 may be use to vary the centralwavelength of the ring filter 642, which requires a feedback from thenode 602. When the RBC count block 640 determines that it is time tovary central wavelength of the ring filter 642 or the BER is greaterthan a threshold, the RBC count block 640 is configured to generate andsend a control signal to the transceiver 630 to vary a centralwavelength of the ring filter 642. The central wavelength of the ringfilter 642 may be varied periodically. The central wavelength of thering filter 642 may be varied based on a data signal frequency of thetransceiver 630. In some embodiments, the central wavelength of the ringfilter 642 may be varied at a frequency at least three orders slowerthan the data signal frequency. The central wavelength of the ringfilter 642 may be varied according to the control mechanism explained inconnection with FIGS. 4A and 4B.

FIG. 7 is a block diagram illustrating another optical communicationnetwork 700 configured to implement the techniques disclosed herein forreducing BER, according to one embodiment. The optical communicationnetwork 700 includes a first node 702 and a second node 704. The firstnode 702 and the second node 704 are connected through optical cables707 a, 706 b. It should be understood that more nodes may be included inthe optical communication network 700. Although shown as separatecables, the optical cables 706 a, 706 b may be combined as a singleduplex cable.

The first node 702 includes transceivers (e.g., optical transceivers oroptical transceiver modules “XCV”) 710, 712 and an ASIC 714. The ASIC714 includes a data output block (Data Out) 716, a data input (Data In)block 718, an RBC Count block 720, and a BER Count block 721. The RBCCount block 720 is coupled to the transceiver 710 to control dataoutput, while the BER Count block 721 is coupled to the transceiver 712to control data input. The transceivers 710 and 712 include ring filters722 and 724, respectively. The data output block 716 of the ASIC 714 isconfigured to generate electrical signals to be transmitted by thetransceiver 710. The electrical signals are converted into opticalsignals at the transceiver 710 and transmitted through the ring filter722 to the second node 704 via the optical cable 706 a. In someembodiments, each of the transceivers 710, 712 may be implemented bysilicon photonic technologies.

The RBC block 720 is configured to keep a count of data output for thenode 702. For example, the RBC block 720 may keep a rolling average ofnumbers of contiguous digital signals (1's or 0's) in a bitstream over aperiod of a predetermined bits (e.g., 1000 bits). The count may be usedto determine a time or times to vary a central wavelength of the ringfilter 722. For example, the central wavelength of the ring filter 722may be varied each time the data output bit count reaches 1000 bits.When the RBC count block 720 determines that it is time to vary centralwavelength of the ring filter 722, the RBC count block 720 is configuredto generate and send a control signal to the transceiver 710 to vary acentral wavelength of the ring filter 722. The central wavelength of thering filter 722 may be varied periodically. The central wavelength ofthe ring filter 722 may be varied based on a data signal frequency ofthe transceiver 710. In some embodiments, the central wavelength of thering filter 722 may be varied at a frequency at least three ordersslower than the data signal frequency.

The transceiver 712 is configured to receive optical signals through thering filter 724 and to convert the received optical signals intoelectrical signals for the ASIC 714. The data input block 718 of theASIC 714 receives the electrical signals from the transceiver 712. Thedata input block 718 may send the electrical signals to other functionalblocks, e.g., the BER count block 721, of the ASIC 714 for processing.The BER block 721 is configured to determine a BER for the receivedsignals based on data input at the data input block 718. When the BER isgreater than a threshold, the BER count block 721 is configured togenerate and send a control signal to the transceiver 712 to vary acentral wavelength of the ring filter 724. For example, once the BERcount block 721 determines that the BER of the incoming signals isgreater than a threshold, the BER count block 721 may provide a controlsignal to the transceiver 712 to periodically vary a central wavelengthof the ring filter 724. The central wavelength of the ring filter 724may be varied based on a data signal frequency of incoming data signals.In some embodiments, the central wavelength of the ring filter 724 maybe varied at a frequency at least three orders slower than the datasignal frequency.

Similarly, the second node 704 includes transceivers (e.g., opticaltransceivers or optical transceiver modules “XCV”) 730, 732 and an ASIC734. The ASIC 734 includes a data output block 736, a data input block738, an RBC Count block 740, and a BER Count block 741. The RBC Countblock 740 is coupled to the transceiver 730 to control data output fromthe second node 704, while the BER Count block 741 is coupled to thetransceiver 732 to control data input to the second node 704. Thetransceivers 730 and 732 include ring filters 742 and 744, respectively.The data output block 736 of the ASIC 734 is configured to generateelectrical signals to be transmitted by the transceiver 730. Theelectrical signals are converted into optical signals at the transceiver730 and transmitted through the ring filter 742 to the first node 702via the optical cable 706 b. In some embodiments, each of thetransceivers 730 and 732 may be implemented by silicon photonictechnologies.

The RBC block 740 is configured to keep a count of data output for thenode 704. For example, the RBC block 740 may keep a rolling average ofnumbers of contiguous digital signals in a bitstream over a period of apredetermined bits (e.g., 1000 bits). The count may be used to determinea time or times to vary a central wavelength of the ring filter 742. Forexample, the central wavelength of the ring filter 742 may be variedeach time the data output bit count reaches 1000 bits or other suitablebits. When the RBC count block 740 determines that it is time to varycentral wavelength of the ring filter 742, the RBC count block 740 isconfigured to generate and send a control signal to the transceiver 730to vary a central wavelength of the ring filter 742. The centralwavelength of the ring filter 742 may be varied periodically. Thecentral wavelength of the ring filter 742 may also be varied based on adata signal frequency of the transceiver 730. In some embodiments, thecentral wavelength of the ring filter 742 may be varied at a frequencyat least three orders slower than the data signal frequency.

The transceiver 732 is configured to receive optical signals through thering filter 744 and to convert the received optical signals intoelectrical signals for the ASIC 734. The data input block 738 of theASIC 734 receives the electrical signals from the transceiver 732. Thedata input block 738 may send the electrical signals to other functionalblocks, e.g., the BER count block 741, of the ASIC 734 for processing.The BER block 741 is configured to determine a BER for the receivedsignals based on data input at the data input block 738. When the BER isgreater than a threshold, the BER count block 741 is configured togenerate and send a control signal to the transceiver 732 to vary acentral wavelength of the ring filter 744. For example, once the BERcount block 741 determines that the BER of the incoming signals isgreater than a threshold, the BER count block 741 may provide a controlsignal to the transceiver 732 to periodically vary a central wavelengthof the ring filter 744. The central wavelength of the ring filter 744may be varied based on a data signal frequency of incoming data signals.In some embodiments, the central wavelength of the ring filter 744 maybe varied at a frequency at least three orders slower than the datasignal frequency. The central wavelengths of the ring filters 722, 724,742, and 744 may be varied according to the control mechanism explainedin connection with FIGS. 5A and 5B.

In some embodiments, the optical communication network 700 may furtherinclude a management server 750 to coordinate efforts to reduce BER. Forexample, the nodes 702 and 704 may exchange the BERs generated by theBER blocks 721 and 741 through the manage server 750 such that each ofthe nodes can use the feedback BERs at the receiver ends to vary thecentral wavelengths of the ring filters 722 and 742 at the transmitterends.

FIG. 8 is a block diagram of a ring filter 800 according to one exampleembodiment. The ring filter 800 may be any one of the ring filters inFIGS. 1, 6, and 7. The ring filter 800 includes a control circuit 802, aphotodetector 804, a heater 806, a diode 808, and a ring cavity 810. Thecontrol circuit 802 is coupled to a node ASIC (e.g., ASIC 114 or 134) toreceive a control signal therefrom. Based on the control signal, thecontrol circuit 802 is configured to generate one or more signals tovary a central wavelength of the ring cavity 810. For example, thecontrol circuit 802 may generate a sinusoidal time-varying signal forone or both of the heater 806 and the diode 808 to vary the centralwavelength of the ring cavity 810. The sinusoidal time-varying signalmay periodically activate the heater 806 and/or the diode 808 to providethermal effects or plasma effects on the ring cavity 810 such that thecentral wavelength of the ring cavity 810 is changed. The thermaleffects or plasma effects may change a dielectric constant of a materialof the ring cavity for varying the central wavelength of the ring cavity810.

In some implementations, the control circuit 802 may generate analternative time-varying signal for one or both of the heater 806 andthe diode 808. The alternative time-varying signal may be a ramp signal.In one instance, the alternative time-varying signal can periodicallymove the central wavelength of the ring cavity 810 away from a carrierfrequency by an offset. The alternative time-varying signal may alsomove the central wavelength of the ring cavity 810 at a first speed atthe carrier frequency and at a second speed at the offset such that thefirst speed is greater than the second speed. This allows the resonantfrequency to spend more time at the offset and less time at the carrierfrequency, which may increase the power of the received signals asexplained above.

The ring cavity 810 has an optical input port (Opt In) 812, an opticaloutput port (Drop Out) 814, and a pass-through port (Thru Out) 816. Theoptical input port 812 is configured to receive input optical signalsfor the optical cavity 810. Optical signals designated for the ringfilter 800 are filtered at the optical output port 814 and can bedetected by the photodetector 804. In some embodiments, thephotodetector 804 may be a photodiode. Optical signals designated fortransit are filtered at pass-through port 816 to be transmitted to adestination.

In summary, the techniques disclosed herein help ameliorate the spectralfiltering that is fundamental to optical links that use ringfilters/resonators. As described above in connection with FIGS. 2A and2B, when a static ring filter is used at the receiver or transmitter,attenuation of the optical sidebands causes deleterious effects on thehigh-speed optical signals. The disclosed techniques add back thisfrequency content is to slowly, with respect to the speed of the datasignal, vary the wavelength of resonance for the receiver ring filter orthe wavelength of carrier signals for the transmitter ring filter.

As used herein, a circuit might be implemented utilizing any form ofhardware, software, or a combination thereof. For example, one or moreprocessors, controllers, ASICs, PLAs, PALs, CPLDs, FPGAs, logicalcomponents, software routines or other mechanisms might be implementedto make up a circuit. In implementation, the various circuits describedherein might be implemented as discrete circuits or the functions andfeatures described can be shared in part or in total among one or morecircuits. Even though various features or elements of functionality maybe individually described or claimed as separate circuits, thesefeatures and functionality can be shared among one or more commoncircuits, and such description shall not require or imply that separatecircuits are required to implement such features or functionality.

In general, the word “component,” “engine,” “system,” “database,” datastore,” and the like, as used herein, can refer to logic embodied inhardware or firmware, or to a collection of software instructions,possibly having entry and exit points, written in a programminglanguage, such as, for example, Java, C or C++. A software component maybe compiled and linked into an executable program, installed in adynamic link library, or may be written in an interpreted programminglanguage such as, for example, BASIC, Perl, or Python. It will beappreciated that software components may be callable from othercomponents or from themselves, and/or may be invoked in response todetected events or interrupts. Software components configured forexecution on computing devices may be provided on a computer readablemedium, such as a compact disc, digital video disc, flash drive,magnetic disc, or any other tangible medium, or as a digital download(and may be originally stored in a compressed or installable format thatrequires installation, decompression or decryption prior to execution).Such software code may be stored, partially or fully, on a memory deviceof the executing computing device, for execution by the computingdevice. Software instructions may be embedded in firmware, such as anEPROM. It will be further appreciated that hardware components may becomprised of connected logic units, such as gates and flip-flops, and/ormay be comprised of programmable units, such as programmable gate arraysor processors.

In common usage, the term “or” should always be construed in theinclusive sense unless the exclusive sense is specifically indicated orlogically necessary. The exclusive sense of “or” is specificallyindicated when, for example, the term “or” is paired with the term“either,” as in “either A or B.” As another example, the exclusive sensemay also be specifically indicated by appending “exclusive” or “but notboth” after the list of items, as in “A or B, exclusively” and “A and B,but not both.” Moreover, the description of resources, operations, orstructures in the singular shall not be read to exclude the plural.Conditional language, such as, among others, “can,” “could,” “might,” or“may,” unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or steps.

Terms and phrases used in this document, and variations thereof, unlessotherwise expressly stated, should be construed as open ended as opposedto limiting. Adjectives such as “conventional,” “traditional,” “normal,”“standard,” “known,” and terms of similar meaning should not beconstrued as limiting the item described to a given time period or to anitem available as of a given time, but instead should be read toencompass conventional, traditional, normal, or standard technologiesthat may be available or known now or at any time in the future. Thepresence of broadening words and phrases such as “one or more,” “atleast,” “but not limited to” or other like phrases in some instancesshall not be read to mean that the narrower case is intended or requiredin instances where such broadening phrases may be absent.

What is claimed is:
 1. An optical transceiver module comprising: anoptical transceiver having a ring filter configured to transmit opticalsignals from or receive optical signals transmitted to the opticaltransceiver module; and a controller configured to: detect a carrierfrequency at the optical transceiver; detect a data signal frequency ofdata at the optical transceiver, the data signal frequency being lessthan the carrier frequency; determine a bit error rate of the data; andin response to determining that the bit error rate of the data isgreater than a threshold, periodically vary a central wavelength of thering filter at a frequency at least three orders slower than the datasignal frequency.
 2. The optical transceiver module of claim 1, furthercomprising: a heater disposed at the ring filter, wherein the controllercontrols the heater to periodically vary the central wavelength of thering filter.
 3. The optical transceiver module of claim 2, wherein: theheater is periodically heated to provide a thermal effect to vary thecentral wavelength of the ring filter.
 4. The optical transceiver moduleof claim 1, further comprising: a diode disposed at the ring filter,wherein the controller controls the diode to periodically vary thecentral wavelength of the ring filter.
 5. The optical transceiver moduleof claim 4, wherein: the diode is configured to provide a plasma effectto vary the central wavelength of the ring filter.
 6. The opticaltransceiver module of claim 1, wherein the controller is configured toprovide a sinusoidal time-varying signal to vary the central wavelengthof the ring filter.
 7. The optical transceiver module of claim 1,wherein the controller is configured to provide an alternativetime-varying signal to vary the central wavelength of the ring filter.8. The optical transceiver module of claim 7, wherein the alternativetime-varying signal includes a ramp signal.
 9. The optical transceivermodule of claim 7, wherein the alternative time-varying signalperiodically moves the central wavelength of the ring filter away fromthe carrier frequency by an offset.
 10. The optical transceiver moduleof claim 9, wherein the alternative time-varying signal moves thecentral wavelength of the ring filter at a first speed at the carrierfrequency and at a second speed at the offset, wherein the first speedis greater than the second speed.
 11. An optical communication networkcomprising: an optical transmitter; an optical receiver; and one or moreoptical cables connected between the optical transmitter and the opticalreceiver, wherein each of the optical transmitter and the opticalreceiver includes: a ring filter; and a controller configured to: detecta carrier frequency at the optical transmitter or the optical receiver;detect a data signal frequency of data at the optical transmitter or theoptical receiver, the data signal frequency being less than the carrierfrequency; determine a bit error rate of the data; and in response todetermining that the bit error rate of the data is greater than athreshold, periodically vary a central wavelength of the ring filter ata frequency at least three orders slower than the data signal frequency.12. The optical communication network of claim 11, further comprising: aheater disposed at the ring filter, wherein the controller controls theheater to periodically vary the central wavelength of the ring filter.13. The optical communication network of claim 12, wherein: the heateris periodically heated to provide a thermal effect to vary the centralwavelength of the ring filter.
 14. The optical communication network ofclaim 11, further comprising: a diode disposed at the ring filter,wherein the controller controls the diode to periodically vary thecentral wavelength of the ring filter.
 15. The optical communicationnetwork of claim 14, wherein: the diode is configured to provide aplasma effect to vary the central wavelength of the ring filter.
 16. Theoptical communication network of claim 11, wherein the controller isconfigured to provide a sinusoidal time-varying signal to vary thecentral wavelength of the ring filter.
 17. The optical communicationnetwork of claim 11, wherein the controller is configured to provide analternative time-varying signal to vary the central wavelength of thering filter.
 18. The optical communication network of claim 17, whereinthe alternative time-varying signal includes a ramp signal.
 19. Theoptical communication network of claim 17, wherein the alternativetime-varying signal periodically moves the central wavelength of thering filter away from the carrier frequency by an offset.
 20. Theoptical communication network of claim 19, wherein the alternativetime-varying signal moves the central wavelength of the ring filter at afirst speed at the carrier frequency and at a second speed at theoffset, wherein the first speed is greater than the second speed.